This invention relates to a method for consolidating an oil-bearing matrix by use of solidifying or consolidating material together with a combustion promoter and an oxidizing agent to produce a coke-like residue for the consolidation.
The recovery of crude oil or natural gas from underground deposits through wellbores assumes the presence of a bed of storage or reservoir rock in the pores or fissures of which the oil or gas can be trapped or collected. As a rule the reservoir rock consists of sand, clay or chalk sediments cemented together by clay, chalk or silicate binders. If this cement, which links together the particles of the supporting structure, is missing either in whole or in part, then one may speak of unconsolidated or poorly consolidated reservoir rocks. In places where the supporting action of neighboring particles or grains in an agglomeration of particles or grains is missing as, for example, in an "open hole" or wellbore, the reservoir rocks tend to subside and under the influence of the transverse action exerted by flowing liquids or gases the grains may be carried away. Both, production wells and injection wells may be affected seriously by the presence of sand grains in the liquid causing erosion of the bore hole installations, stopping of the sucker rod pumps or blocking of the flow channels.
In order to counteract these problems, special sand consolidating methods have been developed, all of which have the following characteristics in common: a fluid, wetting substance is forced into the matrix or rock formation, the substance being such that through the effect of a catalyst or of the temperature it solidifies. It displaces the contents of the pores and wets the surface of the rock particles with a film. In the intergranular pore spaces a liquid meniscus forms and is held firm by capillary effects. The excess liquid from the pores is displaced by a gas or liquid in order to maintain the permeability of the rock which is to be consolidated. After the solidifying substance has hardened, those grains which have been wetted by the substance are bonded or cemented together.
Polymerizing substances have hitherto often been used as the hardening or consolidating material. They have either been mixed with a catalyst (hardener) or hardened by the action of temperature. For example, epoxy resin or formaldehyde and a phenolic compound have been used. In order to remove the superfluous chemicals, diesel oil has normally been used as an after-wash fluid.
It is the object of the invention to provide an improvement in the known processes of hardening or consolidating unconsolidated sediments, strata or formations.
The object is achieved by a process for hardening unconsolidated or insufficiently consolidated sediments, which process is characterized in that residual oil in the formation is mixed with a material which promotes the combustion of the solidifying material. An after-wash fluid may then be injected to wash away the excess material and to restore the permeability of the formation or bed. Thereafter the mixture is brought into contact with an oxidizing agent in order to form a hard deposit or residue in the intergranular spaces of the matrix.